Installation of Tex Live did not solve a missing package problem

I'm writing this after literally half a day of trying.

Ever since I installed Ubuntu (couple of weeks ago) and up until now, I've been using TeXstudio 2.6.6 for writing latex documents.

I didn't have to install anything for it to compile and generate basic mathematical Latex documents.

But I was trying this morning to plot the graph of the equation x^2+y^2=5 on an x–y cartesian coordinate system (the circle with centre coordinates (0, 0) and radius 5), when I found out that I'm missing a package that could help me doing that: pgfplots.

This started an exhausting search that took almost 5 hours, while I was trying to understand how on earth to install this package.

So it all started with a post I found online, saying I need tlmgr in order to install new packages. this turns out later to have a partial support for my Ubuntu version (14.04), and required some more dependencies (at least I think that's what it was...) installation.

After doing that, I tried to install the package with:

 tlmgr install pgfplots

That failed for a reason that was revealed an hour later: tlmgr "needs to be initialized" with:

tlmgr init-usertree

After doing that, I tried again tlmgr install pgfplots, which raised an error, saying I need to install xzdec.

Again, having no idea what I'm installing, I ran:

sudo apt-get install xzdec

And when I though my misery is finally over, I tried to install it again.

But that also raised some error (I don't remember what that was).

Looking again for an answer online, I found out this: http://ift.tt/19qV5Qu so I installed it too!

It took a while, but it seemed promising at first, because it looked like it was doing some work, and downloading tons of packages to /usr/local/texlive/2014/texmf-dist/ (the package pgfplots being one of them).

When it was finished, it said there to add /usr/local/texlive/2014/texmf-dist/doc/info to my INFOPATH and /usr/local/texlive/2014/texmf-dist/doc/man to my MANPATH and "most importantly" it said to add /usr/local/texlive/2014/bin/x86_64-linux to my PATH, and so I did, but when I now open TeX Studio, it still says "\usepackage{pgfplots} Package not found" and "File `pgfplots.sty' not found." !

Please, if I'm getting something wrong help me understand what it is.

Let's start with:

If Tex Live (the thing that I installed) is, and I quote:

an easy way to get up and running with the TeX document production system. It provides a comprehensive TeX system with binaries for most flavors of Unix, including GNU/Linux, and also Windows.

and I just installed it this very moment, then how was I able to write Latex documents on TeX Studio up until now?

The second thing I'm confused about:

If Tex Live is now installed, and I know that I have the package pgfplots on my machine (I saw it when Tex Live was showing me the installation progress), then why is Tex Studio still complaining it can't find this package?

Any help regarding these two questions will be greatly appreciated.

And I don't mean to sound rude, but please, please, please, don't tell me "you need X and Y to be able to run Z on W to solve this problem", but rather give me specific instructions ("Open X, move file Y to Z, run W from terminal..."). And please, please, please, don't tell me "you can find the answer in this link to the (200 pages of) documentation" but rather link me to the specific page in it discussing this issue.

Thank you for reading, any help would be greatly appreciated.